Protective housing for an integrated optical component

ABSTRACT

The optical component  4! consists of a substrate made of an optical material that carries at least one integrated waveguide and that is extended beyond the said substrate by optical fibers exiting from the protective housing  1!  3! for the component. The housing defines a closed internal cavity  2! in which the said component  4! is placed. In accordance with the invention, the said cavity  2! is sized such as to hold the component  4! with a certain amount of play  j i  ! that prevents any significant transmission of stresses between the housing  1!  3! and the component  4!.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon French Patent Application No. 95/01862,filed Feb. 7, 1995, the content of which is relied upon and incorporatedherein by reference in its entirety, and the benefit of priority under35 U.S.C. § 119 i hereby claimed.

BACKGROUND OF THE INVENTION

The present invention relates to a protective housing for an opticalcomponent and, more specifically, to such a housing that has beendesigned to protect a component that consists of a substrate made of anoptical material that carries at least one integrated waveguide and thatis extended, beyond the said substrate, by optical fibers exiting fromthe housing, which defines a closed internal cavity in which the saidcomponent is placed.

RELATED ART

In particular, such housings are used to protect integrated opticalcomponents such as couplers or multiplexers associated with fiber opticsfor the long-distance transmission of digital or analog information ofthe type used for example in applications such as audio, video, or dataprocessing. The integrated optical components take the form of a plateor a bar made of a crystalline material or an amorphous opticalmaterial, such as glass, with waveguides that have been formed forexample by the diffusion of ions being embedded under one surface of theplate or the bar. The ends of the waveguides are connected to opticalfibers that exit from the housing that protects the component.

Such a component is fragile and must be protected effectively from theapplication of mechanical stresses and constraints that could break it,and from other physical or chemical phenomena that could damage it,including particularly variations in temperature or contact with watercaused by the humidity of the air. For these reasons the component iscurrently enclosed within a hermetically sealed and rigid container,with a photosetting or thermosetting resin filling the space left freeinside the housing by the component, in order to prevent any entry ofmoist air or air that contains other damaging ingredients. It canreadily be understood how, when such a set of different and integrallyjoined materials is subjected to broad variations in temperature, suchas the ones that are imposed by the test standards applicable to thesecomponents, the stresses and constraints caused by differential thermalexpansions can break the component located inside the housing.

In order to remedy this disadvantage, in European patent No. 106 116 itwas proposed that the component be mounted inside the housing on asupport made of a material that has the same coefficient of thermalexpansion as the glass, such as the iron-nickel alloy known under thename of INVAR ™, with this support in turn being attached to a tubularscreen made of the same material. The result is a fairly complexprotective structure that contains a large number of parts to beassembled.

SUMMARY OF THE INVENTION

The goal of the present invention is to provide a protective housing foran integrated optical component, with this housing being designed insuch a way as to prevent damage to, or breakage of, this component as aresult of the effect of stresses and constraints of various origins, andparticularly the ones that are caused by differential thermalexpansions, while still having a simple structure and lending itself toautomatic assembly and closure.

These goals of the invention, along with others that will become clearfrom a reading of the following description, are obtained through aprotective housing for an optical component that consists of a substratemade of an optical material that includes at least one integratedwaveguide and that is extended, beyond the said substrate, by opticalfibers that exit from the housing, which housing defines a closedinternal cavity in which the said component is placed, with this housingbeing notable in that the said cavity is sized such as to hold the saidcomponent with an amount of play that prevents any significanttransmission of stress, strain, or pressure between the house and thecomponent.

Because of this amount of play, the housing is uncoupled or isolatedfrom the optical component in terms of the transmission of anymechanical stresses applied to the housing by handling, vibratingsupports, attachment straps, etc., or by differential thermalexpansions. Thus, this uncoupling protects the fragile component fromthe application of such stresses that are capable of breaking ordamaging it.

In accordance with a preferred embodiment of the invention, the housingincludes at least one flexible unit that is pressed lightly between twosurfaces facing the component and the cavity in the housing, in order toprevent any potential vibrations of the component in the cavity.

BRIEF DESCRIPTION OF DRAWINGS

Other characteristics and advantages of the housing in accordance withthe invention will become clear from a reading of the followingdescription and an examination of the attached drawing, on which:

FIG. 1 is a partial longitudinal cross-sectional view of the housing inaccordance with the invention, fitted with the integrated opticalcomponent that it protects;

FIG. 2 is a partial view of the bottom of the housing shown in FIG. 1,taken along the sectional line II--II in FIG. 1;

FIG. 3 represents a perspective view of a watertight joint that formspart of the housing in accordance with the invention, and

FIGS. 4 and 5 are transverse cross-sectional views of the housing inaccordance with the invention, in the pre-assembly position and in theassembled position, respectively.

DETAILED DESCRIPTION OF THE INVENTION

Reference shall now be made to FIGS. 1 and 2 on the attached drawing, inwhich partial cross-sectional views of the housing in accordance withthe invention have been provided. The housing is oblong in shape andsymmetrical overall in relation to a plane P, and thus displays twoends, as represented in these figures.

The housing includes essentially a base 1! that contains a cavity 2!which is generally parallelepipedal and closed by a lid 3!. The lidcontains a recess 3₁ ! that is suitable for receiving a self-adhesivelabel that identifies the component contained in the housing. The cavity2! in the base is shaped so as to receive an integrated opticalcomponent 4! whose shape is generally complementary. This component istraditionally produced with the aid of a substrate made of an opticalmaterial, such as glass, or a crystalline material. Waveguides 6₁ ! 6₂ !6₃ !, etc., produced for example through ion diffusion, are embeddedunder the upper surface 5! of the component (see FIG. 2). Each of theends of the guides is connected to one end of a bare optical fiber 7₁ !7₂ ! 7₃ !, etc., with this fiber being covered by a protective envelope8₁ ! 8₂ ! 8₃ !, etc. before exiting from the housing between twowatertight joints 9₁ ! and 9₂ !. The connection of each fiber to the endof the corresponding waveguide can be ensured by a drop of an adhesiveproduct 10₁ ! while another, larger drop of an adhesive product 11!ensures the mechanical bond between the substrate and the set of fibers

Such an integrated optical component is well known, for example, throughFrench patent application No. 2 674 033, filed by the present applicant.Such a component may consist of a coupler with M inputs and N outputs,or else a multiplexer, in which case the number of fibers that exit fromone end of the housing is generally different from the number of fibersthat exit from the other end of the same housing.

In accordance with an important characteristic of the present invention,the cavity 2! formed in the housing is sized such as to hold thecomponent 4! with an amount of mechanical play that prevents allsignificant transmission of stresses between the base 1! and the cover3! of the housing, on the one hand, and the integrated optical component4!, on the other hand. Thus, due to the fact that the component issimply placed in the cavity 2! without being affixed there by anadhesive product, the component does not form an integral part of thehousing, and each of these two elements can then expand freely inrelation to one another in the event of variations in temperature,thereby eliminating all application to the component 4! of stressescaused by differential expansions that could damage or even break thecomponent.

The uncoupling makes it possible to select, as a construction materialfor the housing, a material that is well suited, for example, from thepoint of view of its resistance to shocks or impacts, or because of itsability to be molded without any need to take into consideration (inpractical terms) its coefficient of thermal expansion. Thus, forexample, a product could be selected that consists of a liquid-crystalpolymer filled with fiberglass, such as the product designated by thename VECTRA A 130 in the catalogues of HOECHST AG And Hoechst CelaneseCorporation, or else a polycarbonate.

The amount of play necessary for the uncoupling can be provided allaround the component. For example, a certain amount of play j_(i) !could be provided between the two facing end surfaces of the componentand of the housing, with a different amount of play j₂ ! being providedbetween the component and the cover 3! (see FIG. 1), and two otheramounts of play j_(i) ! and j₄ ! being provided between the facinglongitudinal surfaces (see FIG. 2). As an indicative and non-limitativeexample, for a component that occupies 50 ×5×5 mm of space, each of theamounts of play j_(i) ! could be on the order of approximately 0.3 mm.

Although the presence of these amounts of play make it possible to solvethe problem consisting of the absorption of differential thermalexpansions, nevertheless under certain circumstances they make possiblethe vibration of the component inside the housing, as a result of forexample of periodic stresses applied to the support to which the housingis attached.

In accordance with a preferred embodiment of the invention, thesevibrations are prevented through the provision, in the cavity of thehousing, of at least one flexible unit that is shaped in such a way asto be pressed between one surface of the component and one facing wallof the cavity, with an amount of force that is great enough to opposeany initiation of the vibration of the component while remaining smallenough to avoid re-establishing a transmission path for the mechanicalstresses to which the housing is exposed, or a transmission path for thestresses caused by differential thermal! expansions.

This unit may advantageously be in the shape of a flexible lip 12! thatis molded as a unit with the base 2! of the housing and shaped so as toextend slightly into the cavity in the absence of the component 4!.Several such lips may be provided, for example, two on each of thelongitudinal walls of the cavity, as can be seen in FIG. 2. In avariant, the forces developed by these lips may be different, in orderto oppose any resonances that may occur as a result of vibrationsapplied to the housing.

In another variant, these lips may be replaced by flexible ribs 13!, asshown by dashed lines in FIG. 1, formed on two facing longitudinal wallsof the cavity. The ribbing advantageously has a triangular cross-sectionand a chamfer 13₁ ! at the head, in order to facilitate the insertion ofthe component 4! into the base 1! of the housing.

FIG. 3 shows a preferred embodiment of the watertight joints 9₁ ! and 9₂! mounted in the recesses in the cover 3! and in the base 1! of thehousing, respectively, provided to receive these joints. These joints,which are identical and made of a flexible material (such as for examplean elastomer with a very low modulus of elasticity), have a series ofgutters 14₁ ! 14₂ ! 14₃ !, etc., that are parallel and generallysemi-cylindrical, each of which adapts closely to one of the fibers inits protective envelope 8₁ ! 8₂ ! 8₃ !, etc. in a flat ribbon exitingfrom the housing. With a pair of such joints clamping the ribbon, thephysical watertightness of the housing at the point at which the fibersenter and exit is ensured. Thanks to the nature of the material of whichthey are made, these joints do not however prevent a slow migration ofwater vapor, from the inside of the housing toward the outside, when thetemperature inside the housing may cause an increase in the relativepressure of this water vapor to a value that may be damaging to thecomponent.

As shown in FIGS. 1 and 2, the outlets of these entries and exits towardthe outside of the housing have rounded profiles 15₁ ! 15₂ ! 15₃ !,etc., in the plane of the ribbons (see FIG. 2) and also in a plane thatis orthogonal to the latter plane (see FIG. 1). Thus, the fibers thatexit from the housing can be drawn in directions that diverge from thedirection of their axes inside the housing (See the position indicatedby a dashed line in FIG. 1), with confidence that the change indirection will be consistent with a certain minimum radius of curvaturer (i.e., the radius of curvature of the rounded area against which thefiber rests) that is sufficient to prevent any breakage of the fiber.For example, a radius r=2 mm may be selected.

The base 1! and the cover 3! of the housing may be obtained through themolding of a plastic material and assembled as indicated below, duringthe course of the assembly of the unit consisting of the opticalcomponent and its protective housing.

After the bare fibers 7₁ ! have been connected to the ends of thewaveguides that form an integral part of the substrate of thiscomponent, by means of well-known operations consisting of themicro-manipulation of the fibers and the deposition of drops ofadhesives, the component is inserted into the cavity 2! in the base 1!,with care being taken to ensure that the portions of the fibers locatedunder the fiber envelope 8_(i) ! pass through the gutters 14_(i) ! inthe two joints 9₁ ! 9₂ ! located at the two ends of the base 1!. Awater-repellent lubricant, for example, of the so-called"mechanical"type or having a base of silicone, may be injected into thespace that separates the component 4! from the walls of the cavity 2!,to reinforce the resistance of the component to the moisture present inthe air and to other damaging agents that may be carried by this air.This injection should be made with the allowance of an expansion volumefor the lubricant, so as to prevent any overpressure effect associatedwith the expansion of the lubricant.

The cover 3! is then inserted into the base 1!, in the pre-assemblyposition shown diagrammatically in FIG. 4. In this figure it can be seenthat several clamping tabs 16₁ ! 16₂ ! extend from the cover in order topenetrate into corresponding slots 17₁ ! 17₂ ! formed in the base, asfar as just beyond a peripheral ribbing 18!, which the clamping tabpasses because of its flexibility, and which then holds the cover 3!onto the base 1!, slightly above the later, in a position that allowsthe cover to be removed easily, if necessary, for example to check orinspect the installation of the component in the housing.

This pre-assembly step makes it possible to handle easily the resultingassembly, until the cover is welded (in a procedure not shown) onto thebase, for example, by ultrasonic welding. During this stage the cover isheld by an ultrasonic head that places it in the final welding positionshown in FIG. 5, which is a view along sectional line V--V in FIG. 1,while transmitting to the lid the proper ultrasonic vibrations forensuring the welding of the cover 3! to the base 1! at the position oftheir peripheral surfaces that are in contact, indicated in this figureby reference 19!.

It is clear that all of these operations lend themselves to automationof the process consisting of the mounting of the component in itshousing.

It is now clear that the invention makes it possible for the establishedgoals to be reached, i.e., through the provision of a protective housingfor an integrated optical component that is protected from the effectsof possible differential thermal expansions or the mechanical stressesto which the housing may be subjected, with this housing retaining asimple structure that is suitable for the automation of the assemblyoperations.

Of course, the invention is not limited to the embodiments described andrepresented herein, which have been provided only as examples.

We claim:
 1. Protective housing for an optical component 4!, consistingof a substrate made of a material carrying at least one integratedwaveguide 6_(i) ! that is extended beyond said substrate by opticalfibers 7_(i) ! exiting from the housing, with said housing defining aclosed internal cavity 2! in which said component 4! is placed,characterized by the fact that said cavity 2! is sized such as to holdsaid component with a certain amount of play j_(i) ! that prevents asignificant transmission of stresses between the housing and thecomponent 4!.
 2. Housing in accordance with claim 1, characterized bythe fact that it contains at east one flexible unit 12! 12'! 13! that ispressed slightly between two facing surfaces of the component 4! and ofthe cavity 2! in the housing 1! 3! in order to prevent potentialvibrations of the component 4! in the cavity 2!.
 3. Housing inaccordance with claim 2, characterized by the fact that said flexibleunit is in the form of a lip 12! 12'! that is formed as a unit with thewall of the housing 1! 3! and that extends beyond one surface of thecavity 2! formed in this housing.
 4. Housing in accordance with claim 2,characterized by the fact that said flexible unit is in the form of aflexible ribbing 13! formed on one wall of the cavity 2! in the housing.5. Housing in accordance with any one of claims 1 to 4, characterized bythe fact that it includes a base 1! in which the cavity 2! is formed,and a cover 3! that closes said cavity 2!, with said cover 3! beingprovided with a plurality of clamping tabs 16_(i) ! designed tocooperate with complementary ribbing 18! in the base 1!, in order toensure a temporary pre-assembly of the cover 3! and of the base 1! in arelative position that is different from the one that corresponds totheir permanent assembly.
 6. Housing in accordance with claim 5,characterized by the fact that the cover 3! has, on its outer surface, arecess 3₁ ! suitable for receiving a label.
 7. Housing in accordancewith claim 6, characterized by the fact that the base 1! and the cover3! receive, in the area where the housing 1! 3! is crossed by theoptical fibers 7_(i) ! 8_(i) !, watertight joints 9₁ ! 9₂ ! that aresuitable for receiving in a complementary way the fibers 7_(i) ! 8_(i) !in the form of a flat ribbon.
 8. Housing in accordance with any one ofclaims 1 to 4 or 6, characterized by the fact that it has roundedsurfaces 15_(i) ! located at the points at which the optical fibers exitthe housing, with said rounded surfaces being suitable for supportingthe fibers by means of a pre-determined minimum radius of curvature (r).9. Housing in accordance with any one of claims 1 to 4 or 6-7, providedwith an integrated optical component 4!.
 10. Housing in accordance withclaim 9, characterized by the fact that a water-repellent lubricant isprovided in the space that separates the component 4! from the wall ofthe cavity 2!.